Field of the Invention
Exemplary embodiments of the present invention relate to a piston oil-up prevention; and, particularly, to a method for preventing a piston oil-up and an engine which is employing the method, wherein a hard carbon formation can be prevented with the aid of a quick oil suction using a pump under an oil-up formation condition of the engine.
Description of Related Art
In general, a piston oil-up may cause a hard carbon formation during a combustion in case of a high load since an engine oil moves upward through a gap between a piston ring and a cylinder.
In a commercially available CNG (Compressed Natural Gas) engine, an idle operation may cause an oil-up due to a negative pressure formation (Max. −0.7 bar) at an intake manifold and the cylinders of the engine. A long time idle operation would worsen such an oil-up due to the oil pressure which in general is higher than the pressure at an oil jet check valve, and a coasting condition would also worsen the oil-up due to a quick negative pressure formation at the intake manifold under a condition where a load is not being applied. As a result, the above-mentioned oil-up may cause many problems, for example, a carbide may be adhered to a piston and a lower surface of a head during the supply of the load since oil is inputted through a piston clearance, and particles which have separated during an opening and closing operation of an exhaust valve may cause dents between the exhaust valve and the head, thus resulting in the melting (or burning) of the valve if the above-mentioned situation worsens and worsens repeatedly.
For this reason, a commercially available CNG (Compressed Natural Gas) engine has a function to minimize any oil-up in such a way to improve an oil consumption at a low speed section/a high speed section with the aid of piston and ring pack specification improvements.
Since a trade-off relationship exists between the above-mentioned low speed section wherein it is more advantageous if an oil consumption of the engine is less and the above-mentioned high speed section wherein an appropriate oil supply is required, there may be an inevitable limit when trying to improve the oil-up through the piston and ring pack specification improvements.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.